46 GRASSHOPPERS IN GENERAL. 



The blood of insects differs from that of other animals in having no- 

 red corpuscles. It is a thin fluid and, being a mixture of blood and 

 chyle, usually colorless, but sometimes yellowish or reddish. It i& 

 carried forward by this tube or heart to the front end, and then flow& 

 back, nourishing the organs as it passes, and likewise coming in con- 

 tact with tracheae, which are everywhere present in the body. When 

 in contact with these tracheae, action similar to that in the human 

 lung takes place. More will be said upon this phase of the subject 

 under the head of the "Respiratory system." It will be seen that 

 the chief function of this heart is to conduct forward newly made 

 blood and unused blood from the back end of the body, pour it out at 

 the front end of the body, and allow it to flow back like a river in its- 

 course. This action of the heart can be seen with the naked eye in 

 some caterpillars with light color and delicate skin, when held be- 

 tween the observer and the sun. 



FIG. 26. (Original.) Respiratory system, ftp., spiracles, showing tracheae permeating all parts 

 of the body ; tf, air sacs. Enlarged three times. 



Respiratory system. This insect, instead of having one portion of 

 the body set apart for the purification of the blood, similar to ani- 

 mals possessing lungs, may be said to have lungs all over its system ; 

 that is, there are tracheae branched and branched until they cover 

 every part of the system and extend to every organ in the system. 

 These tracheae do not depend upon the mouth for their supply of air, 

 but are connected with the body wall direct, the outer portion of this 

 connection being known as spiracles (figs. 21, 27). These spiracles 

 have valves and openings which close and open at intervals, allowing 

 free interchange of air. The tracheae which run from these spiracles 

 are membranous tubes, which do not collapse because they are kept 

 open by continuous rings of cartilage similar, though on a much smaller 

 scale, to the cartilage in the windpipe of those animals bearing lungs. 

 In addition to carrying to all parts of the body, it would seem that 

 this distribution of air within the body tends to make the insect 

 .lighter and more capable of flight. In addition to these tracheae, 



